Memory cell sensing using a boost voltage

ABSTRACT

The present disclosure includes devices, methods, and systems including memory cell sensing using a boost voltage. One or more embodiments include pre-charging and/or floating a data line associated with a selected memory cell, boosting the pre-charged and/or floating data line, and determining a state of the selected memory cell based on a sensed discharge of the data line after boosting the data line.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor memorydevices, methods, and systems, and more particularly, to memory cellsensing using a boost voltage.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits and/or external removable devices in computers orother electronic devices. There are many different types of memoryincluding random-access memory (RAM), read only memory (ROM), dynamicrandom access memory (DRAM), synchronous dynamic random access memory(SDRAM), phase change random access memory (PCRAM), and flash memory,among others.

Flash memory devices can be utilized as volatile and non-volatile memoryfor a wide range of electronic applications. Flash memory devicestypically use a one-transistor memory cell that allows for high memorydensities, high reliability, and low power consumption. Uses for flashmemory include memory for solid state drives (SSDs), personal computers,personal digital assistants (PDAs), digital cameras, cellulartelephones, portable music players (e.g., MP3 players) and movieplayers, among other electronic devices. Data, such as program code,user data, and/or system data, such as a basic input/output system(BIOS), are typically stored in flash memory devices.

Two common types of flash memory array architectures are the “NAND” and“NOR” architectures, so called for the logical form in which the basicmemory cell configuration of each is arranged. A NAND array architecturearranges its array of memory cells in a matrix such that the controlgates of each memory cell in a “row” of the array are coupled to (and insome cases form) an access line, which is commonly referred to in theart as a “word line”. However each memory cell is not directly coupledto a data line (which is commonly referred to as a digit line, e.g., abit line, in the art) by its drain. Instead, the memory cells of thearray are coupled together in series, source to drain, between a commonsource and a data line, where the memory cells commonly coupled to aparticular data line are referred to as a “column”.

Memory cells in a NAND array architecture can be programmed to a target(e.g., desired) state. For example, electric charge can be placed on orremoved from a charge storage structure of a memory cell to put the cellinto one of a number of programmed states. For example, a single levelcell (SLC) can represent two states (e.g., 1 or 0). Flash memory cellscan also store more than two states (e.g., 1111, 0111, 0011, 1011, 1001,0001, 0101, 1101, 1100, 0100, 0000, 1000, 1010, 0010, 0110, and 1110).Such cells can be referred to as multilevel cells (MLCs). MLCs can allowthe manufacture of higher density memories without increasing the numberof memory cells since each cell can represent more than one digit (e.g.,more than one bit). For example, a cell capable of representing fourdigits can have sixteen programmed states.

A state of a flash memory cell can be determined by sensing the storedcharge on the charge storage structure (e.g., the threshold voltage) ofthe cell. The threshold voltage (Vt) of the cell can be a positive ornegative voltage. That is, the cell can be programmed to a positive or anegative Vt level.

Sensing operations (e.g., read and/or program verify operations) can usesensing voltages to sense the Vt of flash memory cells and therebydetermine the state of the cells. For example, to sense the Vt anddetermine the state of a cell programmed to a negative Vt level, asensing operation can include applying a negative sensing voltage to acontrol gate of the cell, for instance. However, to generate thenegative sensing voltage, additional and/or complex circuitry, such as,for instance, a negative voltage pump and/or isolated devices, may beneeded. Such additional and/or complex circuitry needed to generate anegative sensing voltage can, for example, increase the size, increasethe power consumption, and/or decrease the performance of a memorydevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a portion of a non-volatile memory array inaccordance with one or more embodiments of the present disclosure.

FIG. 2 illustrates a timing diagram associated with a sensing operationin accordance with a previous approach.

FIG. 3 illustrates a timing diagram associated with a sensing operationin accordance with one or more embodiments of the present disclosure.

FIG. 4 illustrates a diagram of a number of threshold voltagedistributions in accordance with a previous approach.

FIGS. 5A-5C illustrate a diagram of a number of threshold voltagedistributions in accordance with one or more embodiments of the presentdisclosure.

FIG. 6 illustrates a block diagram of a memory device in accordance withone or more embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure includes devices, methods, and systems includingmemory cell sensing using a boost voltage. One or more embodimentsinclude pre-charging and/or floating a data line associated with aselected memory cell, boosting the pre-charged and/or floating dataline, and determining a state of the selected memory cell based on asensed discharge of the data line after boosting the data line.

Embodiments of the present disclosure can be used to determine the stateof memory cells having (e.g., programmed to) a negative thresholdvoltage (Vt) level without applying a negative sensing voltage to thecell. Determining the state of memory cells having a negative Vt levelwithout applying a negative sensing voltage to the cells can providebenefits such as decreasing the size, decreasing the power consumption,and/or increasing the performance of a memory device, among otherbenefits.

Additionally, embodiments of the present disclosure can be used todetermine the state of memory cells having negative Vt levels of greatermagnitudes than previous approaches such as source side sensing and/orback bias sensing, for instance. Accordingly, embodiments of the presentdisclosure can provide the ability to sense memory cells having a widerrange of Vts than such previous approaches, among other benefits.

In the following detailed description of the present disclosure,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration how a number of embodimentsof the disclosure may be practiced. These embodiments are described insufficient detail to enable those of ordinary skill in the art topractice the embodiments of this disclosure, and it is to be understoodthat other embodiments may be utilized and that process, electrical,and/or structural changes may be made without departing from the scopeof the present disclosure.

As used herein, “a number of” something can refer to one or more suchthings. For example, a number of memory devices can refer to one or morememory devices. Additionally, the designators “N” and “M” as usedherein, particularly with respect to reference numerals in the drawings,indicates that a number of the particular feature so designated can beincluded with a number of embodiments of the present disclosure.

The figures herein follow a numbering convention in which the firstdigit or digits correspond to the drawing figure number and theremaining digits identify an element or component in the drawing.Similar elements or components between different figures may beidentified by the use of similar digits. For example, 100 may referenceelement “00” in FIG. 1, and a similar element may be referenced as 600in FIG. 6. As will be appreciated, elements shown in the variousembodiments herein can be added, exchanged, and/or eliminated so as toprovide a number of additional embodiments of the present disclosure. Inaddition, as will be appreciated, the proportion and the relative scaleof the elements provided in the figures are intended to illustrate theembodiments of the present disclosure, and should not be taken in alimiting sense.

FIG. 1 is a schematic of a portion of a non-volatile memory array 100 inaccordance with one or more embodiments of the present disclosure. Theembodiment of FIG. 1 illustrates a NAND architecture non-volatile memoryarray. However, embodiments described herein are not limited to thisexample. As shown in FIG. 1, the memory array 100 includes access lines(e.g., word lines 105-1, . . . , 105-N) and intersecting data lines(e.g., local bit lines 107-1, 107-2, 107-3, . . . , 107-M). For ease ofaddressing in the digital environment, the number of word lines 105-1, .. . , 105-N and the number of local bit lines 107-1, 107-2, 107-3, . . ., 107-M can be some power of two (e.g., 256) word lines by 4,096 bitlines.

Memory array 100 includes NAND strings 109-1, 109-2, 109-3, . . . ,109-M. Each NAND string includes non-volatile memory cells 111-1, . . ., 111-N, each communicatively coupled to a respective word line 105-1, .. . , 105-N. Each NAND string (and its constituent memory cells) is alsoassociated with a local bit line 107-1, 107-2, 107-3, . . . , 107-M. Thenon-volatile memory cells 111-1, . . . , 111-N of each NAND string109-1, 109-2, 109-3, . . . , 109-M are connected in series source todrain between a source select gate (SGS) (e.g., a field-effecttransistor (FET)) 113, and a drain select gate (SGD) (e.g., FET) 119.Each source select gate 113 is configured to selectively couple arespective NAND string to a common source 123 responsive to a signal onsource select line 117, while each drain select gate 119 is configuredto selectively couple a respective NAND string to a respective bit lineresponsive to a signal on drain select line 115.

As shown in the embodiment illustrated in FIG. 1, a source of sourceselect gate 113 is connected to a common source line 123. The drain ofsource select gate 113 is connected to the source of the memory cell111-1 of the corresponding NAND string 109-1. The drain of drain selectgate 119 is connected to bit line 107-1 of the corresponding NAND string109-1 at drain contact 121-1. The source of drain select gate 119 isconnected to the drain of the last memory cell 111-N (e.g., afloating-gate transistor) of the corresponding NAND string 109-1.

In one or more embodiments, construction of the non-volatile memorycells 111-1, . . . , 111-N includes a source, a drain, a floating gateor other charge storage structure, and a control gate. The non-volatilememory cells 111-1, . . . , 111-N have their control gates coupled to aword line, 105-1, . . . , 105-N respectively. A “column” of thenon-volatile memory cells, 111-1, . . . , 111-N, make up the NANDstrings 109-1, 109-2, 109-3, . . . , 109-M, and are coupled to a givenlocal bit line 107-1, 107-2, 107-3, . . . , 107-M, respectively. A “row”of the non-volatile memory cells are those memory cells commonly coupledto a given word line 105-1, . . . , 105-N. The use of the terms “column”and “row” is not meant to imply a particular linear (e.g., verticaland/or horizontal) orientation of the non-volatile memory cells. A NORarray architecture would be similarly laid out, except that the stringof memory cells would be coupled in parallel between the select gates.

As one of ordinary skill in the art will appreciate, subsets of cellscoupled to a selected word line (e.g., 105-1, . . . , 105-N) can beprogrammed and/or sensed (e.g., read) together as a group. A programmingoperation (e.g., a write operation) can include applying a number ofprogram pulses (e.g., 16V-20V) to a selected word line in order toincrease the threshold voltage (Vt) of selected cells coupled to thatselected access line to a desired program voltage level corresponding toa target program state.

A sensing operation, such as a read or program verify operation, caninclude sensing a voltage and/or current change of a bit line associatedwith (e.g., coupled to) a selected cell in order to determine the stateof the selected cell. For instance, the sensed voltage and/or currentcan correspond to a particular Vt level of the memory cell, which cancorrespond to one of a number of states. Sensing operations inaccordance with one or more embodiments of the present disclosure willbe further described below.

FIG. 2 illustrates a timing diagram 201 associated with a sensingoperation in accordance with a previous approach. For instance, timingdiagram 201 illustrates a number of voltage waveforms (e.g., voltagewaveforms 221, 223, and 225) that can be associated with a back biassensing approach.

Waveform 221 represents a voltage signal applied to a source line (e.g.,a source voltage) associated with a selected memory cell during asensing operation. At a time t1, the source line is increased to sourcevoltage 222. However, previous approaches, such as a back bias sensingoperation, may limit source voltage 222 to a particular maximum voltagein order to maintain a suitable drain to source voltage differenceassociated with the memory cell. As an example, a back bias sensingoperation may include pre-charging the bit line of the selected cell toa supply voltage (e.g., Vcc) level of about 2.3 V, for instance, suchthat the Vcc voltage is applied to the drain of the cell. As such, thesource voltage is limited to less than the 2.3 V Vcc level. Forinstance, source voltage 222 may be limited to a voltage not greaterthan about 1.5 V to 1.8 V, in order to maintain a drain to sourcevoltage different of greater than about 0.4 V to 0.6 V.

Waveform 223 represents a voltage signal applied to a data lineassociated with the selected memory cell during the back bias sensingoperation illustrated in FIG. 2. At a time t2, the data line isincreased to a voltage 224. That is, the data line is pre-charged tovoltage 224. Voltage 224 can have, for example, a magnitude equal to thesum of source voltage 222 and a data line clamp voltage (Vclamp), whichcan be used to clamp the data line voltage 224 to a particular level.

Waveform 225 represents a voltage signal applied to a source select gate(SGS) and a drain select gate (SGD) associated with the selected memorycell during the sensing operation. At a time t3, the SGS and SGD areincreased to a voltage 226. Voltage 226 can have, for example, amagnitude equal to the sum of source voltage 222 and a select gatevoltage (e.g., Vsg).

At time t3 (e.g., when the select gate waveform 225 transitions from lowto high), the data line associated with the selected memory cell maybegin to discharge, as represented by the dashed line illustrated inFIG. 2. At a time t4 (e.g., when the select gate waveform 225transitions from high to low), the state of the selected memory cell canbe determined based on the sensed discharge of the data line. That is,the state of the selected memory cell can be determined based on thedischarge of the data line as determined by a sense amplifier, forinstance.

During the back bias sensing operation illustrated in FIG. 2, a tubregion and/or a well region of the semiconductor substrate associatedwith the selected memory cell may be grounded. For instance, a voltageof 0 V may be applied to the tub region and/or the well region of thesemiconductor substrate during the sensing operation.

FIG. 3 illustrates a timing diagram 302 associated with a sensingoperation in accordance with one or more embodiments of the presentdisclosure. Timing diagram 302 illustrates a number of voltage waveforms(e.g., voltage waveforms 331, 333 and 337). The sensing operation can beperformed on an array of memory cells, such as, for example, array 100previously described in connection with FIG. 1.

Waveform 331 represents a voltage signal applied to a data lineassociated with a selected memory cell during a sensing operation inaccordance with one or more embodiments of the present disclosure. At atime t1, the data line is pre-charged to a pre-charge voltage 332.Pre-charge voltage 332 can be a positive voltage such as, for example,0.5 V. After time t1, the pre-charged data line can be floated, in oneor more embodiments.

The selected memory cell can have (e.g., be programmed to) a negativethreshold voltage (Vt). For example, the selected memory cell can have aVt of between 0 V and −5.5 V. In one or more embodiments in which the Vtof a selected memory cell is negative, the cell can be associated with astate having only negative Vts associated therewith. However,embodiments of the present disclosure are not so limited. For instance,embodiments of the present disclosure can be used to sense memory cellshaving a Vt associated with a state having both negative and positive Vtlevels associated therewith.

Waveform 333 represents a voltage signal applied to a source lineassociated with the selected memory cell during the sensing operation.At a time t2, the source line is boosted (e.g., increased) to boostvoltage 334. Applying boost voltage 334 to the source line (e.g.,increasing the source line to boost voltage 334) at time t2 can resultin the pre-charged and/or floating data line being boosted frompre-charge voltage level 332 to a boosted data line voltage 336. Thatis, boosting the source line can boost the pre-charged and/or floatingdata line.

In contrast, in previous approaches, the data line associated with theselected memory cell is not pre-charged and/or floating when a sourcevoltage (e.g., source voltage 222) is applied to the source lineassociated with the selected memory cell, as previously describedherein. Rather, in previous approaches, a boosted source voltage (e.g.,source voltage 222) is applied to the source line prior to apre-charging or floating of the data line, as previously describedherein.

Unlike the source voltage 222 previously described in connection withFIG. 2, the boosted source voltage 334 may not be limited to a voltagelevel below a particular voltage (e.g., Vcc). For instance, since thedata line is boosted to a voltage 336, which is greater than the boostedsource voltage 334, the boosted source voltage 334 can have a valueequal to Vcc, for example. In one or more embodiments, the boostedsource voltage 334 can be equal to a Vcc of about 2.4 V. However,embodiments of the present disclosure are not limited to a particularvoltage 334. For instance, the voltage 334 can be greater or less thanabout 2.4 V, and may not be a Vcc voltage.

Applying boost voltage 334 to the source line can boost (e.g., increase)the voltage of the pre-charged data line to voltage 336. Voltage 336 canbe the sum of the magnitude of the pre-charge voltage 332 and the boostvoltage 334, in one or more embodiments. Because both pre-charge voltage332 and boost voltage 334 can be positive voltages, voltage 336 (e.g.,the sum of the magnitude of the pre-charge voltage 332 and the boostvoltage 334) can be greater than boost voltage 334.

In some embodiments, a tub region and/or the well region of thesemiconductor substrate associated with the selected memory cell can beincreased to boost voltage 334 at time t2. Alternatively, in someembodiments, a ground voltage (e.g., 0 V) may be applied to the tubregion and/or the well region of the semiconductor substrate during thesensing operation.

Waveform 337 represents a voltage signal applied to a source select gate(SGS) and a drain select gate (SGD) associated with the selected memorycell during the sensing operation. At a time t3, the SGS and the SGD areincreased to a voltage 338. Voltage 338 can have, for example, amagnitude equal to the sum of boost voltage 334 and a select gatevoltage (e.g., Vsg). Voltage 338 can be greater than voltage 336 (e.g.,voltage 338 can be greater than the sum of pre-charge voltage 332 andboost voltage 334), as illustrated in FIG. 3.

At time t3 (e.g., when the select gate waveform 337 transitions from lowto high), the data line associated with the selected memory cell maybegin to discharge, as represented by the dashed lines illustrated inFIG. 3. The discharge of the data line may be (e.g., occur) in responseto a discharge of the source line associated with the selected memorycell at time t3. That is, a discharge of the source line can be causedat time t3, and the data line may discharge in response to the dischargeof the source line.

At a time t4 (e.g., when the select gate waveform 337 transitions fromhigh to low), the state of the selected memory cell can be determinedbased on the sensed discharge of the data line associated with theselected memory cell. For example, the state of the selected memory cellcan be determined based on the discharge of the data line as determinedby a sense amplifier, for instance. The state of the selected memorycell can be, for example, a programmed state.

Accordingly, sensing operations in accordance with one or moreembodiments of the present disclosure can determine the state of theselected memory cell without applying a negative voltage to the cell.For example, sensing operations in accordance with one or moreembodiments of the present disclosure can determine the state of theselected memory cell without applying a negative voltage to an accessline associated with the selected memory cell. Rather, sensingoperations in accordance with one or more embodiments of the presentdisclosure can determine the state of the selected memory cell byapplying only positive voltages (e.g., positive voltages 332, 334, 336,and 338) to the cell. Determining the state of the selected memory cellwithout applying a negative voltage to the cell can provide benefitssuch as decreasing the size, decreasing the power consumption, and/orincreasing the performance of a memory device, among other benefits.Further, one or more embodiments of the present disclosure can providethe ability to determine the states of memory cells having a negative Vtgreater in magnitude than previous approaches, which can provide anincreased programming window, among other benefits.

FIG. 4 illustrates a diagram 403 of a number of threshold voltagedistributions in accordance with a previous approach. The example shownin FIG. 4 can represent, for example, a number of two-bit (e.g.,four-state) non-volatile memory cells.

As shown in FIG. 4, threshold voltage (Vt) distributions 445-0, 445-1,445-2, and 445-3 represent four target states (e.g., L0, L1, L2, and L3,respectively) to which the memory cells can be programmed. As shown inFIG. 4, diagram 403 includes a range of voltage levels (e.g., Vmin toVmax) to which the Vts of the memory cells can be programmed in order torepresent the different target states.

In operation, the memory cells in a selected block can be erasedtogether such that they have a Vt level within Vt distribution 445-0prior to being programmed. As such, distribution 445-0 can be referredto as an erased state and can represent a particular stored data state(target state L0, e.g., stored data such as binary “11”). Target stateL1 can correspond to data 01, target state L2 can correspond to data 00,and target state L3 can correspond to data 10. However, previousapproaches are not limited to these data assignments.

Vt distributions 445-0, 445-1, 445-2, and 445-3 can represent a numberof memory cells that are programmed to the corresponding target states,where the height of a Vt distribution curve indicates a number of cellsprogrammed to a particular voltage within the Vt distribution, onaverage. The width 447 of the Vt distribution curve indicates the rangeof voltages that represent a particular target state (e.g., the width ofthe Vt distribution curve 445-2 for L2 represents the range of voltagesthat correspond to data 00).

Sensing operations in accordance with one or more previous approachespreviously described herein (e.g., in connection with FIG. 2) can beperformed to determine the state of the memory cells having a Vt (e.g.,programmed) within the Vt distributions illustrated in FIG. 4. Forexample, sensing operations using the waveforms (e.g., waveforms 221,223, and 225) and/or voltages (e.g., voltages 222, 224, and 226)associated with timing diagram 201 previously described in connectionwith FIG. 2 can be performed to distinguish between states L0, L1, L2,and L3 illustrated in FIG. 4.

However, sensing operations in accordance with one or more previousapproaches previously described herein (e.g., in connection with FIG. 2)may not be able to determine the state of a memory cell having (e.g.,programmed to) a Vt of less than −1.5 V. Accordingly, Vmin illustratedin FIG. 4 (e.g., the lowest Vt to which a memory cell may be programmedin such previous approaches) may not be less than −1.5 V. That is, thelower limit of the range of voltage levels to which the Vts of thememory cells can be programmed in such previous approaches may not beless than −1.5 V.

FIGS. 5A-5C illustrate a diagram 504 of a number of threshold voltagedistributions in accordance with one or more embodiments of the presentdisclosure. The examples shown in FIGS. 5A-5C can represent, forexample, memory cells 111-1, . . . , 111-N previously described inconnection with FIG. 1. The examples shown in FIGS. 5A-5C representtwo-bit (e.g., four-state) memory cells. However, embodiments of thepresent disclosure are not limited to this example of two-bit memorycells.

As shown in FIGS. 5A-5C, threshold voltage (Vt) distributions 555-0,555-1, 555-2, and 555-3 represent four target states (e.g., L0, L1, L2,and L3, respectively) to which the memory cells can be programmed. Asshown in FIGS. 5A-5C, diagram 504 includes a range of voltage levels(e.g., Vmin to Vmax) to which the Vts of the memory cells can beprogrammed in order to represent the different target states.

In operation, the memory cells in a selected block can be erasedtogether such that they have a Vt level within Vt distribution 555-0prior to being programmed. As such, distribution 555-0 can be referredto as an erased state and can represent a particular stored data state(target state L0, e.g., stored data such as binary “11”). Target stateL1 can correspond to data 01, target state L2 can correspond to data 00,and target state L3 can correspond to data 10. However, embodiments ofthe present disclosure are not limited to these data assignments.

Vt distributions 555-0, 555-1, 555-2, and 555-3 can represent a numberof memory cells that are programmed to the corresponding target states,where the height of a Vt distribution curve indicates a number of cellsprogrammed to a particular voltage within the Vt distribution, onaverage. The width 557 of the Vt distribution curve indicates the rangeof voltages that represent a particular target state (e.g., the width ofthe Vt distribution curve 555-2 for L2 represents the range of voltagesthat correspond to data 00).

Sensing operations in accordance with one or more embodiments of thepresent disclosure can be performed to determine the state of the memorycells having a Vt (e.g., programmed) within the Vt distributionsillustrated in FIGS. 5A-5C. For example, sensing operations using thewaveforms (e.g., waveforms 331, 333, and 337) and/or voltages (e.g.,voltages 332, 334, 336, and 338) associated with timing diagram 302previously described in connection with FIG. 3 can be performed todistinguish between states L0, L1, L2, and L3 illustrated in FIGS.5A-5C.

Sensing operations in accordance with one or more embodiments of thepresent disclosure can determine the state of a memory cell having(e.g., programmed to) a Vt of less than −1.5 V (e.g., to a Vt of −5.5V). In contrast, sensing operations in accordance with previousapproaches may not be able to determine the state of a memory cellhaving a Vt of less than −1.5 V, as previously described herein.

Accordingly, Vmin illustrated in FIGS. 5A-5C (e.g., the lowest Vt towhich a memory cell may be programmed in accordance with one or moreembodiments of the present disclosure) can be less than −1.5 V (e.g.,can be −5.5 V). That is, the lower limit of the range of voltage levelsto which the Vts of the memory cells can be programmed in accordancewith one or more embodiments of the present disclosure can be less than−1.5 V (e.g., can be −5.5 V). In contrast, the lower limit of the rangeof voltage levels to which the Vts of the memory cells can be programmedin accordance with previous approaches may not be less than −1.5 V, aspreviously described herein.

Because sensing operations in accordance with one or more embodiments ofthe present disclosure can determine the state of memory cellsprogrammed to a Vt of less than −1.5 V (e.g., to a Vt of −5.5 V),sensing operations in accordance with one or more embodiments of thepresent disclosure can sense memory cells having a wider range of Vtsthan sensing operations in accordance with previous approaches. Forexample, sensing operations in accordance with one or more embodimentsof the present disclosure can determine the state of memory cells havingnegative Vt levels of greater magnitudes than sensing operations inaccordance with previous approaches.

For example, as illustrated in the example shown in FIG. 5A, Vtdistribution 555-0 (e.g., the erased state) can include negative Vts ofgreater magnitude than the negative Vts of Vt distribution 445-0 (e.g.,the erased state) previously described in connection with FIG. 4.Accordingly, Vt distribution 555-1 (e.g., the L1 state) can include bothpositive and negative Vts, as illustrated in the example shown in FIG.5B, or only negative Vts, as illustrated in the example shown in FIG.5C. In contrast, Vt distribution 445-1 (e.g., the L1 state) previouslydescribed in connection with FIG. 4 may include only positive Vts. Thatis, Vt distribution 445-1 may not be able to include any negative Vts,as illustrated in FIG. 4.

FIG. 6 illustrates a block diagram of a memory device 660 in accordancewith one or more embodiments of the present disclosure. As shown in FIG.6, memory device 660 includes a memory array 600 and a controller 662coupled to memory array 600.

Memory array 600 can be, for example, memory array 100 previouslydescribed in connection with FIG. 1. Although one memory array is shownin FIG. 6, embodiments of the present disclosure are not so limited(e.g., memory device 660 can include more than one memory array coupledto controller 662).

Controller 662 can include, for example, control circuitry and/orfirmware. For instance, controller 662 can include sense circuitry 664,as illustrated in FIG. 6. Controller 662 can be included on the samephysical device (e.g., the same die) as memory array 600, or can beincluded on a separate physical device that is communicatively coupledto the physical device that includes memory array 600.

Sense circuitry 664 can perform sensing operations in accordance withone or more embodiments of the present disclosure to determine the stateof the memory cells in memory array 600. For example, sense circuitry664 can perform sensing operations on the memory cells in memory array600 using the waveforms (e.g., waveforms 331, 333, and 337) and/orvoltages (e.g., voltages 332, 334, 336, and 338) associated with timingdiagram 302 previously described in connection with FIG. 3.

Sense circuitry 664 can be standard (e.g., unchanged) sense circuitry.For example, sense circuitry 664 may not include negative voltagecircuitry (e.g., circuitry that can generate a negative sensingvoltage). Such sense circuitry can decrease the size, decrease the powerconsumption, and/or increase the performance of memory device 660, amongother benefits.

The embodiment illustrated in FIG. 6 can include additional circuitrythat is not illustrated so as not to obscure embodiments of the presentdisclosure. For example, memory device 660 can include address circuitryto latch address signals provided over I/O connectors through I/Ocircuitry. Address signals can be received and decoded by a row decoderand a column decoder, to access memory array 600. It will be appreciatedby those skilled in the art that the number of address input connectorscan depend on the density and architecture of memory device 660 and/ormemory array 600.

CONCLUSION

The present disclosure includes devices, methods, and systems includingmemory cell sensing using a boost voltage. One or more embodimentsinclude pre-charging and/or floating a data line associated with aselected memory cell, boosting the pre-charged and/or floating dataline, and determining a state of the selected memory cell based on asensed discharge of the data line after boosting the data line.

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art will appreciate that anarrangement calculated to achieve the same results can be substitutedfor the specific embodiments shown. This disclosure is intended to coveradaptations or variations of a number of embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. Combinationof the above embodiments, and other embodiments not specificallydescribed herein will be apparent to those of ordinary skill in the artupon reviewing the above description. The scope of a number ofembodiments of the present disclosure includes other applications inwhich the above structures and methods are used. Therefore, the scope ofa number of embodiments of the present disclosure should be determinedwith reference to the appended claims, along with the full range ofequivalents to which such claims are entitled.

In the foregoing Detailed Description, some features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the disclosed embodiments of the presentdisclosure have to use more features than are expressly recited in eachclaim. Rather, as the following claims reflect, inventive subject matterlies in less than all features of a single disclosed embodiment. Thus,the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

What is claimed is:
 1. A method of sensing a memory cell, comprising:pre-charging a data line associated with a selected memory cell;boosting the pre-charged data line by: floating the pre-charged dataline; and applying a boost voltage to a source line associated with aplurality of strings of memory cells, wherein one of the stringsincludes the selected memory cell, while floating the pre-charged dataline; and determining a state of the selected memory cell based on asensed discharge of the data line after boosting the data line.
 2. Themethod of claim 1, wherein: the selected memory cell has a negativethreshold voltage; and the method includes determining the state of theselected memory cell without applying a negative voltage to the selectedmemory cell.
 3. The method of claim 1, wherein the sensed discharge ofthe data line is in response to a discharge of the source line.
 4. Themethod of claim 1, wherein pre-charging the data line includes applyinga pre-charge voltage to the data line.
 5. The method of claim 4, whereinboosting the pre-charged data line increases a voltage associated withthe data line to a sum of the magnitude of the pre-charge voltage and aboost voltage.
 6. A method of sensing a memory cell, comprising:pre-charging a data line associated with a selected memory cell having anegative threshold voltage; boosting the pre-charged data line by:floating the pre-charged data line; and applying a boost voltage to asource line associated with a plurality of strings of memory cells,wherein one of the strings includes the selected memory cell, whilefloating the pre-charged data line; and determining a state of theselected memory cell based on a sensed discharge of the data lineresponsive to boosting the pre-charged data line and without applying anegative voltage to the selected memory cell.
 7. The method of claim 6,wherein determining the state of the selected memory cell includesdetermining the state of the selected memory cell without applying anegative voltage to an access line associated with the selected memorycell.
 8. The method of claim 6, wherein the selected memory cell has athreshold voltage of less than approximately −1.5 Volts.
 9. The methodof claim 8, wherein the selected memory cell has a threshold voltage ofless than approximately −5.5 Volts.
 10. The method of claim 6, whereinthe state of the selected memory cell is an erased state.
 11. The methodof claim 6, wherein the state of the selected memory cell is aprogrammed state.
 12. The method of claim 6, wherein the selected memorycell has a negative threshold voltage that is within a threshold voltagedistribution that includes only negative threshold voltages.
 13. Themethod of claim 6, wherein the selected memory cell has a negativethreshold voltage that is within a threshold voltage distribution thatincludes positive and negative threshold voltages.
 14. A method ofsensing a memory cell, comprising: applying a pre-charge voltage to adata line associated with the selected memory cell; floating thepre-charged data line; boosting the floating data line to a sum of themagnitude of the pre-charge voltage and a boost voltage by applying theboost voltage to a source line associated with a plurality of strings ofmemory cells, wherein one of the strings includes the selected memorycell; causing a discharge of the source line after applying the boostvoltage to the source line; and determining a state of the selectedmemory cell based on a sensed discharge of the data line in response tothe discharge of the source line.
 15. The method of claim 14, whereinthe pre-charge voltage and the boost voltage are positive voltages. 16.The method of claim 14, wherein the sum of the magnitude of thepre-charge voltage and the boost voltage is greater than the boostvoltage.
 17. The method of claim 14, wherein the method includesapplying the boost voltage to a well region of a semiconductor substrateassociated with the selected memory cell while floating the pre-chargeddata line.
 18. The method of claim 14, wherein the method includesapplying the boost voltage to a tub region of a semiconductor substrateassociated with the selected memory cell while floating the pre-chargeddata line.
 19. The method of claim 14, wherein the method includesapplying a voltage that is greater than the sum of the magnitude of thepre-charge voltage and the boost voltage to a drain select gate and asource select gate associated with the selected memory cell whilecausing the discharge of the source line.
 20. The method of claim 14,wherein the boost voltage is at least approximately 2.4 Volts.
 21. Themethod of claim 14, wherein the boost voltage is approximately equal toa supply voltage level.